Mixer trucks used to transport and dispense concrete and similar materials incorporate one or more chutes utilized to convey such material from one location to another. For example, most mixer trucks incorporate a hopper loader chute located at the mixer drum to direct fluent material into the drum. Also, discharge chutes (both primary chutes and extension chutes) are normally employed to convey the concrete or other material from the drum to a location at a work site.
Chutes associated with mixer trucks are subjected to a great deal of wear and tear, not only by the impact and abrasion resulting from movement of the concrete or other fluent material but also by the impact of other machinery or equipment. For example, hopper loader chutes are often struck and damaged by delivery spouts or conveyors utilized when filling the mixer drum. Impact and wear of the chutes will, over a period of time, result in significant deterioration thereof. Another contributing factor to such deterioration is exposure of the chutes to the liquid components of concrete and the like.
In order to avoid, or at least defer, the expenses associated with replacement of old chutes with new, attempts have been made to repair the chutes. One approach has been to weld liners of steel to the chutes. This is an expensive procedure and one which often can be carried out only once. Furthermore, chutes in a significant state of deterioration or chutes of certain types of materials are often not amenable to repair utilizing this approach. Use of steel or other metal liners also adds significant weight to the chute, which is undesirable.
Attempts have been made to coat chutes with plastic material; that is, a bond is created between the plastic and the chute material over the entire extent thereof. This causes difficulties due to the difference in coefficients of expansion of the two materials. Furthermore, any break in the coating will result in the underlying chute material coming into contact with liquid, thus causing rust which will over time significantly deteriorate the quality and strength of the chute. This same result can, of course, occur even when steel liners or plates are affixed to chutes. And it almost goes without saying that the various attempts to protect mixer truck chutes just described result in permanent alteration of the chutes. That is, the various liners and coatings become integral parts of the chutes, rendering further repair even more difficult, if not impossible.
A patentability search directed to the present invention located the following U.S. Pat. Nos.: 5,035,313, issued Jul. 30, 1991, 4,529,660, issued Jul. 16, 1985, 4,645,055, issued Feb. 24, 1987, 4,574,933, issued Mar. 11, 1986, 4,054,194, issued Oct. 18, 1977, 3,150,753, issued Sep. 29, 1964, and 3,508,405, issued Apr. 28, 1970.
Of these patents, U.S. Pat. No. 5,035,313 is worthy of particular comment. U.S. Pat. No. 5,035,313 discloses a dispensinq chute for attachment to a mixer truck comprising a plurality of telescopically mounted sections. The chute sections are in the form of interlocking open metal frames having replaceable plastic liners affixed to the frames in the interior thereof. In other words, the liners, which are secured to the chute frames along the lengths thereof and are not moveable with respect to the frames, are not protective liners at all but rather parts of the chutes themselves.
U.S. Pat. No. 4,054,194 discloses a conveying chute for freshly mixed concrete made from a metal frame having a replaceable polyurethane liner. Again, the liner is a part of the conveyor and not a protective liner for protecting the conveyor. The liner is in the form of a sheet fixedly held to its frame by sets of bolts and nuts at each end of the frame.